In recent years, in a wide range of computer systems ranging from handheld information devices such as cellular phones, a slate terminals or tablet terminals to large-scale systems such as supercomputers, a reduction of system power consumption has become an important issue. As a way of reducing power consumption, for example, a power gating technique of supplying power to only portions (units) which require power is known.
For example, in an idle state where the processor of a computer system executes nothing, it is possible to reduce power consumption by stopping the supply of power to a cache memory in which part of a plurality of pieces of data used for processing by the processor are stored.
The computer system described above generally includes a prefetch (or, pre-fetch) function which involves predicting data which is highly likely to be used by a processor in the near future among a plurality of pieces of data stored in a main storage device and reading out the predicted data in advance onto a cache memory. Here, for example, regardless of the fact that the data read out by prefetch (or, pre-fetch) is stored in a cache memory, when the supply of power to the cache memory is stopped, the data read out onto the cache memory by the prefetch will be removed. Thus, in order to use the data, it is necessary to read out the data again onto the cache memory. As a result, there is a problem in that power used for prefetch is consumed unnecessarily.